String.format("%,d", number)

或

DecimalFormat formatter = new DecimalFormat("#,###,###");
String yourFormattedString = formatter.format(5000);

或

DecimalFormatSymbols otherSymbols = new DecimalFormatSymbols(currentLocale);
otherSymbols.setDecimalSeparator(',');
otherSymbols.setGroupingSeparator('.'); 
DecimalFormat df = new DecimalFormat(formatString, otherSymbols);
currentLocale can be obtained from Locale.getDefault() i.e.:

Locale currentLocale = Locale.getDefault();